1. Field of the Invention
The present invention relates to a device and method for the directional delivery of a biologically active agent. More particularly, the invention relates to a stent made from an elongated member which has a cavity or interior containing an active agent for sustained directional delivery to a predetermined location in a body lumen, such as the wall of the body lumen.
2. Description of the Related Art
Many diseases cause body lumens to undergo stenosis or a narrowing of a canal within the body. Arteriosclerosis refers generally to a group of diseases in which the lumen of a blood vessel becomes narrowed or blocked, which may prevent a sufficient amount of blood from flowing through the blood vessel to the tissue. This shortage of blood flow caused by arteriosclerosis ultimately can permanently damage tissue and organs.
The therapeutic alternatives available for treatment of arteriosclerotic diseases include dilation of the artery using a pharmaceutical, surgical intervention to remove the blockage, replacement of the blocked segment with a new segment of artery, or the use of a catheter-mounted device such as a balloon catheter to dilate the artery. The dilation of an artery with a balloon catheter is called percutaneous transluminal angioplasty. During angioplasty, a balloon catheter in a deflated state is inserted within a stenotic segment of a blood vessel and is inflated and deflated a number of times to expand the vessel. Due to the inflation of the balloon catheter, the plaque formed on the vessel walls cracks and the vessel expands to allow increased blood flow through the vessel.
Often angioplasty permanently opens previously occluded blood vessels; however, restenosis, thrombosis, or vessel collapse may occur following angioplasty. Restenosis refers to the re-narrowing of an artery after an initially successful angioplasty due to exaggerated healing which causes a proliferation of tissue in the angioplasty area. Thrombosis is a clotting within a blood vessel which may cause infarction of tissues supplied by the blood vessel. In order to prevent restenosis and vessel collapse, stents of various configurations have been used to hold the lumen of a blood vessel open following angioplasty. However, stents do not entirely reduce the occurrence of thrombotic abrupt closure due to clotting; stents with rough surfaces exposed to blood flow may actually increase thrombosis, and restenosis may still occur because tissue may grow through and around the lattice of the stent. To prevent restenosis and thrombosis in the area where angioplasty has been performed, antithrombic agents and other biologically active agents can be employed.
Several stents exist which attempt to deliver active agents to the area in which angioplasty was performed. Some of these stents are biodegradable stents which have been impregnated with active agents. Examples of such impregnated stents are those disclosed in U.S. Pat. Nos. 5,500,013; 5,429,634; and 5,443,458. Other known agent delivery stents include a stent disclosed in U.S. Pat. No. 5,342,348 which includes a biologically active agent impregnated in delivery matrix filaments which may be woven into a stent or laminated onto a stent. U.S. Pat. No. 5,234,456 discloses a hydrophilic stent which can include a biologically active agent disposed within the hydrophilic material of the stent.
Other biologically active agent delivery stents are disclosed in U.S. Pat. Nos. 5,201,778; 5,282,823; 5,383,927; 5,383,928; 5,423,885; 5,441,515; 5,443,496; 5,449,382; 4,464,450; and European Patent Application No. 0 528 039. Other active agent delivery devices are disclosed in U.S. Pat. Nos. 3,797,485; 4,203,442; 4,309,776; 4,479,796; 5,002,661; 5,062,829; 5,180,366; 5,295,962; 5,304,121; 5,421,826; and International Application No. WO 94/18906.
Although known biologically active agent delivery stents deliver a biologically active agent to the area in which angioplasty was performed, they do not directionally deliver the active agent and, consequently, much of the biologically active agent is directed into the blood stream and does not reach the blood vessel wall where treatment is needed. Furthermore, these known agent delivery stents may actually increase the possibility of thrombosis. For example, some current stents attempt to reduce the risk of thrombosis by incorporating an extremely smooth and electropolished surface on the stent. However, this surface is ineffective against thrombosis when such stents are coated with a polymeric drug delivery system that is exposed to the bloodstream; the presence of such polymer drug delivery systems on current stents in the path of the bloodstream may actually initiate clotting.
The previously described problems associated with non-directional beneficial agent delivery provided by current agent delivery stents limits their range of effective use. Because of the above identified constraints of current delivery stents, it is very difficult to administer biologically active agents directionally to a desired area of a body lumen. As described above, delivering a biologically active agent to the walls of a blood vessel is problematic because non-directional delivery of the agent using current delivery stents results in much of the agent being carried away with the blood stream. The previously described constraints of current agent delivery stents has created a need for a solution.